Heart valve prostheses are used to replace natural heart valves. Prosthetic heart valves include both mechanical heart valves and tissue or bioprosthetic heart valves. In both types, a valving member is carried in an orifice body or housing. In a mechanical heart valve, the valving member typically comprises a mechanical occluder such as a leaflet movable between an open and a closed position. In a tissue valve, the valving member comprises tissue movable between an open and a closed position.
Such prosthetic heart valve prostheses require the orifice to be attached to the tissue annulus left as a result of the surgical excision of the existing valve from the patient's heart. Typically, a sewing or suture cuff is attached to the valve orifice and is used by a surgeon to suture the prosthesis to the heart tissue. Such attachment requires the ends of the suture to be knotted and cut. Following attachment, the suture knots are exposed to blood flow which can cause postoperative complications, prosthesis thrombosis, thromboembolism, excessive tissue ingrowth, or interfere with operation of the valve mechanism.
The concept of covering heart tissue/valve attachment sutures is not new. The concept was described in 1964 in German Patent Application 1180087, entitled "ARTIFICIAL HEART VALVE," by Dr. Wolfgang Seidel. This publication describes a method of attaching heart valves to the native heart tissue annulus. The attachment method uses a ring, which is partially covered with fabric and has protruding "clips." The orifice and occluder are then placed within the clips. The publication mentions the benefit of covering the suture ends and suture knots to reduce thrombus and thrombo-embolic events. The publication primarily focuses on the valve attachment and the use of solid rings.
A more recent patent application, WO 89/00841, by Lillehei, Wang and Brendzel, entitled "PROTECTIVE SHIELD FOR PROSTHETIC HEART VALVES," was published in 1989. The description in this application is of a protective shield which is annular or ring-shaped to fit over a circular valve base and cover an annular sewing ring. The reference mentions methods of installing the ring and various geometries for this ring. The reference describes a separate attachment ring which is attached using sutures, friction, adhesive, a snap fit, hooks, Velcro.RTM. or conical friction.
Another patent describing sutures and suture knots is U.S. Pat. No. 3,996,623, issued Dec. 14, 1976, to Robert Kaster, entitled "METHOD OF IMPLANTING A PROSTHETIC DEVICE AND SUTURING MEMBER THEREFOR." This reference discusses a cuff configuration which has two cuff flanges. The native heart tissue annulus is captured in the space provided between the two flanges. The cuff has a flexible cured polymer core which provides resilience to the cuff flanges. The surgeon attaches the distal flange to the distal side of the native tissue with sutures and knots. The suture knots would be located on the proximal side of the tissue annulus. While the cuff/valve is being secured to the native tissue with sutures and knots, the proximal cuff is held "open." After the valve is secured, the proximal flange is released to the closed position. The cuff is secured to the orifice using heat Shrink material. This method of attachment has not been readily accepted by surgeons. The current preferred method of attachment is to use a single flanged cuff which is placed on the proximal side of the native tissue annulus.